The First Polish Tektites: Preliminary Sem Investigation

Home , Lechatelierite, Moldavite, Suevite, Tektite

18 Contemporary Trends in Geoscience vol . 2 DOI: 10.2478/ctg-2014-0002

Tomasz Brachaniec1, Krzysztof Szopa1 Łukasz Karwowski1 The first polish tektites: preliminary sem investigation 1 Faculty of Earth Science, University of Silesia, Department of Geochemistry, Mineralogy and Petrography, Bedzinska Str. 60, 41-200 Sosnowiec. E-mails: [email protected], [email protected], [email protected].

Key words: Abstract. tektite, moldavite, In Lower Silesia, the first Polish moldavites strewnfield, were discovered. To recognize the primary crater, Ries, Poland. chemical composition and check the morphology of investigated material SE and BSE images were used. The samples show presence of vesicles, which are one of the most typical features of tektite glass. Referring to the preliminary EDS results and comparing them with literature data, it can be assumed that in all cases the base material for all known moldavites was the same. Contemporary trends in Geoscience vol . 2 19

Introduction The production of impact melt rocks and normal igneous processes (>1713°C; Stöffler glasses is a diagnostic feature for impact iden- 1984) and 3) abundant inclusions of shocked tification. Their presence, distribution, and mineral and lithic fragments are present in mineralogical characteristics have provided impact glasses (e.g. Engelhardt 1972; Grieve valuable information on the cratering process et al. 1977). (e.g. Dence 1971; Grieve et al. 1977; Grieve & Impact glasses from the Ries impact struc- Cintala 1992). A wide variety of impact melt ture have been the subject of many inves- products may be found within and around tigations over the last several decades (e.g. impact craters: 1) crystalline melt bodies in Engelhardt 1967, 1972; Engelhardt et al. 1995; the impact structure; 2) glassy clasts in melt- See et al. 1998; Vennemann et al. 2001). bearing breccias or suevites, within and out- Nowadays, only four tektite strewnfields side the structure; 3) injection dykes in the are recognised (Koeberl 2007 and refer- crater floor and walls; 4) distal ejecta (e.g. ences therein): Central European, North tektites). The majority of these lithologies American, Australasian as well as Ivory represents whole rock melts formed during Coast. The source structure of the first one the shock-induced melting of target rocks impact is crater Ries located in German, in a zone beneath the impact point (Osinski which was dating c.a. 15 Ma. 2003). Impact melt glass may resemble vol- Results of Stöffler et al. (2002) investigation canic glass in appearance; however, several (see also Artemieva 2002) presents a pattern properties can be used to distinguish the two: of moldavite strewnfield in Central Europe. 1) chemical compositions of impact glass- Based on experimental studies simulation es typically match individual lithologies or of the impact Stöffler suggested, that mol- mixtures of different rock types present in davites may be find up to about 525 km from the target sequence (e.g. Dence 1971; Grieve the crater, but this was not confirmed un- 1975; Grieve et al. 1977); 2) the widespread til the Polish discovery of moldvires in late presence of lechatelierite in impact glass- Miocene sediment, Lower Silesia. es indicates temperatures far above those of

Material & Methods Two pieces of moldavites were used for fur- through the atmosphere. This phase, however, ther studies. The first piece of the tektites has did not take place in most of the tektites. In 0.027 g (Fig. 1A) and the second 0.1651 g (Fig. the third phase, after falling on Earth’s sur- 1B). In transmitted light, tektites show a light face, various geological processes finished green color. The present-day shape of the tek- the morphology of the tektites (see discus- tites is not only the result of their formation sion: Trnka & Houzar 2002). caused by impact, but depends on second- Morphology and preliminary chemical ary processes as e.g. weathering, transport, composition of the Polish moldavies was etc. Therefore, Baker (1963) divided the evo- checked by using scanning electron micro- lution of shapes into three stages. First of all, scope Philips XL30 ESEM/TMP equipped the separate bodies of tektites were formed with EDS (EDAX type Sapphire) detector and cooled. In the second, so-called ablation at the Faculty of Earth Sciences, University phase, the shapes were changed by melting of of Silesia. front solid parts during the flight of tektites

SEM investigation The SEM study shows that surface of tek- as a result of internal gas pressure during tites, especially the bigger one is corroded. tektite cooling in environment where the ex- The corrosion is an effect of interaction of ternal pressure was very low (e.g. Suess 1951; the tektite with water and humic substanc- Chao 1963). In fact, several mechanisms of es in the soil (Koeberl et al. 1988). The sam- bubble formation may have been involved. ples show abundant vesicles varying in size As a result of this, even a single tektite sam- from less than 10 µm up to 200 µm (Fig. 1C - ple may contain several populations of bub- F). Most of the vesicles are elongated. bles formed by different mechanisms and Occurrence of vesicles is one of the most containing gases of different compositions typical features for tektite glass. Most au- and pressures (Jessberger & Gentner 1972; thors considered the formation of bubbles see discussion at Zak et al. 2012). 20 Contemporary Trends in Geoscience vol . 2

The chemistry of moldavites, like all tek- (Trnka & Houzar 2002; Zak 2009). According tites and impact glasses, was therefore inter- to Randa et al. (2008) similar contents of Mg preted as a result of melting and incomplete and Ca are evidence of a carbonate origin mixing of several components (Magna et al. of source rocks. The low content of this ele- 2011). The moldavites form the most acidic ments may also be evidence of signature of group of tektites, with SiO2 contents about the ash component. High content of Al was 80 wt% (Trnka & Houzar 2002). no doubt dominated by the clay component EDS analysis shows that Polish moldavites (Randa et al. 2008). It can be preliminary have relatively high and low content of Si02 sugessted that carbonates with lenses of clay and Fe, respectively (Fig. 2A). As it was docu- and small amount of ash were source rocks mented by numerous papers (e.g. Engelhardt of Polish moldavites. et al. 2005) despite the close similarity of the Lechatelierite is present in all samples and chemical composition in terms of the ma- occurs mostly in irregular and elongated jor element contents (Si, Al., Fe, Mg, Ca) of inclusions (Fig. 1F). The structure of the le- moldavites from different substrewnfields, chatelierite in the moldavite glass is an idi- there are some significant differences in cator for rapid and irregular glass flow dur- trace element contents, which bind to dif- ing an early formation stage (Koeberl et al. ferent source rocks (see discussion at Randa 1988). Other mineral inclusions are lack in et al. 2008). Substrewnfields are partial are- the samples. The amount of lechatelierite de- as, that represent a combination of the orig- pends on the temperature conditions of ori- inal distribution in the strewnfield and the gin. Higher temperature caused a lower abun- Fig.1. Polish moldavites. A, B) Macroscop- subsequent removal and redistribution of dance of lechatelierite in Czech and German ic images of studied tektites; C, D, E) The sur- moldavites by fluvial erosion and transport. moldavites (Barnes 1969; Konta 1971a; Lange face of studied moldavites with visible vesicles; F) Lechatelierite inclusions in polish Rare finds of moldavites beyond the limits 1995). Lechatelierite in moldavites is repre- thin section with two types of vesicles: v1 – of the major substrewnfields represent ei- sented by very pure silica (Fig. 2B). Chemical “empty” vesicles, v2 – vesicles fill in epoxy. ther samples transported by surface fluvial analyses show SiO2 contents of above 99 wt.% processes over a long distance or very small (Knobloch 1997). remains of other original substrewnfields

Summary Fig. 2. EDS spectrum for: A) Glass from Polish moldavite, B) Lechatelierite inclu- The discovery of moldavites in Poland shows sion in moldavite, represented by pure that the strewnfield in Central Europe is not silica. confined to the Czech Republic, Austria and Germany but extends further to north-east than previous assumed (Stöffler et al. 2002). EDS analysis of Polish moldavites compared to literature shows a close similarity with other moldavites. This clearly confirm their impact origin. Pre-estimated source rocks of Polish moldavites may have been carbonates with clay minerals. The main aims of further studies are description of moldavite distribution in south-west Poland and chemical as well as isotopic characterization of the new tektites.

References Artemieva, N.A. (2002) Tektite origin in Barnes, V.E. (1969) Petrology of moldavites, oblique impact: Numerical modeling, In: Geochim. Cosmochim. Acta, 33, 1121-1134. Y.Plado and L.Pesonen (eds.) Meteorite Chao, E.C.T. (1963) The petrographic and Impacts in Precambrian Shields, Springer chemical characteristics of tektites, In: Verlag, Berlin, 257-276. J.A.O’Keefe (ed.) Tektites, University Press, Baker, G. (1963) Form and sculpture of 51-94. tektites, In: J.A.O’Keefe (ed.) Tektites, Dence, M.R. (1971) Impact melts, Journal of University Press, 1-24. Geophysical Research, 76, 5552-5565. Contemporary trends in Geoscience vol . 2 Tomasz Brachaniec, Krzysztof Szopa, Łukasz Karwowski 21

The first polish tektites: preliminary sem investigation

Engelhardt, W.v. (1967) Chemical composi- Magna, T., Deutsch, A., Mezger, K., Skala, tion of Ries glass bombs, Geochimica et R., Seitz, H.M., Mizera, J., Randa, Z., Cosmochimica Acta, 31, 1677-1689. Adolph, L. (2011) Lithium in tektites and Engelhardt, W.v. (1972) Shock produced rock impact glasses: Implications for sources, glasses from the Ries crater, Contributions histories and large impacts, Geochimica et to Mineralogy and Petrology, 36, 265-292. Cosmochimica Acta, 75, 2137-2158. Engelhardt, W.v., Arndt, J., Fecker, B., Pankau, Osinski, G.R. (2003) Impact glasses in fall- H.G. (1995) Suevite breccia from the Ries out suevites from the Ries impact struc- crater, Germany: Origin, cooling histo- ture, Germany: An analytical SEM study, ry, and devitrification of impact glasses, Meteoritics & Planetary Science, 38, Meteoritics, 30, 279-293. 1641-1667. Engelhardt, W.v., Berthold, C., Wenzel, T., Randa, Z., Mizera, J., Frana, J., Kucera, J. Dehner, T. (2005) Chemistry, small-scale in- (2008) Geochemical characterization of homogeneity, and formation of moldavites moldavites from a New locality, the Cheb as condensates from sands vaporized by the Basin, Czech Republic, Meteoritics & Ries impact, Geochimica et Cosmochimica Planetary Science, 43, 461-477. Acta, 69, 5611-5626. See, T.H., Wagstaff, J., Yang, V., Hörz, F., Grieve, R.A.F. (1975) Petrology and chemis- McKay G.A. (1998) Compositional vari- try of impact melt at Mistastin Lake crater, ation and mixing of impact melts on mi- Labrador, Geological Society of America croscopic scales, Meteoritics & Planetary Bulletin, 86, 1617-1629. Science, 33, 937-948. Grieve, R.A.F., Cintala, M. J. (1992) An anal- Stöffler, D. (1984) Glasses formed by hyperve- ysis of differential impact crater scaling locity impact, Journal of Non-Crystalline and implications for the terrestrial record, Solids, 67, 465-502. Meteoritics & Planetary Science, 27, Stöffler, D., Artemieva, N.A., Pierazzo, E. 526-538. (2002) Modeling the Ries-Steinheim im- Grieve, R.A.F., Dence, M.R., Robertson, P.B. pact event and the formation of the mol- (1977) Cratering processes: As interpreted davite strewn field, Meteoritics & Planetary from the occurrence of impact melts, In: Science, 37, 1893-1907. D.J. Roddy, R.O.Pepin and R.B.Merrill (eds.) Suess, H.E. (1951) Gas content and age of tek- Impact and explosion cratering, Pergamon tites, Geochimica et Cosmochimica Acta, Press, 791-814. 2, 76-79. Jessberger, E., Gentner, W. (1972) Mass Trnka, M., Houzar, S. (2002) Moldavites: a spectrometric analysis of gas inclusions review, Bulletin of the Czech Geological in Muong Nong glass and Libyan Desert Survey, 77, 283-302. Glass, Earth and Planetary Science Letters, Vennemann, T.W., Morlok, A., Engelhardt, 14, 221-225. W.v., Kyser, K. (2001) Stable isotope compo- Knobloch V. (1997) Nektere problemy vzni- sition of impact glasses from the Nördlinger ku vltavinu III. – Tvary inkluzi a textura ve Ries impact crater, Germany, Geochimica et svetle impaktoveho procesu, Prirodoved. Cosmochimica Acta, 65, 1325-1336. Sbor. Zapadomorav. Muz. v Trebici, 31, Zak, K. (2009) A study of gravel transport 54-60. paths in a stream using metallurgical slag as Koeberl, C. (2007) The geochemistry and cos- a tracer: A contribution to the understanding mochemistry of impacts, In: H.D.Holland of fluvial moldavite redistribution, Bulletin and K.K.Turekian (eds.) Meteorites, com- Mineralogicko-Petrologickeho Oddeleni ets, and planets, Elsevier, 1-52. Narodniho Muzea v Praze, 17, 79-90. Koeberl, C., Brandstatter, F., Niedemmazr, G., Zak, K., Skala, R., Randa, Z., Mizera, J. (2012) Kurat, G. (1988) Moldavites from Austria, A review of volatile compounds in tektites, Meteoritics, 23, 325-332. and carbon content and isotopic compo- Konta, J. (1971a) Shape analysis of moldavites sition of moldavite glass, Meteoritics & and their impact origin, Mineral. Mag., 38, Planetary Science, 47, 1010-1028. 408-417. Lange J.M. (1995) Lausitzer Moldavite und ihre Fundschichten. Schrift, Geowissenschaften, 3, Berlin.